Gait Improvements After Peroneal or Tibial Nerve Transfer in Patients with Foot Drop: A Retrospective Study.

Background: Injury to the common peroneal nerve disrupts the motor control pathway to ankle dorsiflexors and evertors, as well as toe extensors, resulting in pathological gait and foot drop. Direct external compression on the fibular head is the most frequent cause of peroneal nerve impairment and has poor prognosis. Methods and Patients: Here, we report the surgical outcome of 21 patients with foot drop (9 males and 12 females) who underwent nerve transfer procedure of either the superficial peroneal nerve or the tibial nerve fascicles to the motor branch of the tibialis anterior and to the deep peroneal nerve. They had at least 6 months postoperative follow-up (mean = 17; range, 6-32 months). Results: Among 21 patients who had no ankle dorsiflexion (BMRC 0/5) preoperatively, 9 patients had successful restoration of ankle dorsiflexion (BMRC 4 to 4+/5), 7 patients had BMRC 2 to 3+/5, and 4 patients had no or poor restoration of dorsiflexion (BMRC 0 to 1+/5) but achieved good ankle eversion (BMRC 3 to 4+/5). Overall statistically significant clinical improvement of ankle dorsiflexion and eversion from preoperative BMRC grade 2.6 ± 0.5 to postoperative BMRC grade 3.6 ± 0.7 (P = .0000004) was achieved. Conclusion: Overall statistically significant clinical improvement of ankle dorsiflexion and eversion was achieved in 80% of our study patients. Most of these patients gained antigravity and were able to walk with minimal steppage gait. In the other 4 patients (20%), there was good improvement in ankle eversion but poor or no ankle dorsiflexion.


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However, direct external compression on the fibular head is the most common cause of this impairment.
Peroneal nerve damage can occur due to accident, gunshot wound, sciatic nerve tumor, radiculopathy, and hip and knee replacement surgery in numerous pathologies such as stroke, spinal cord injury, multiple sclerosis, and cerebral palsy. Generally, these impairments are complex to manage successfully. The treatment strategies vary according to the nature and level of the nerve damage and planned depending on the underlying pathology.
Several management techniques, including surgical (nerve transfer/grafting, and tendon transfers) and nonsurgical treatments (ankle-foot orthosis [AFO]), have been adopted to improve the failed gait and dropped foot. Nerve stimulators are used 5,6 if the patient has the intact functioning peroneal nerve. If there is no evidence of functional recovery, surgical exploration is necessary and performed at 3 to 7 months from injury. 7,8 Surgical procedure and time of intervention also depend on the type and degree of injury. Laceration or open wounds of the peroneal nerve undergo immediate surgical exploration. 9 Other lesions are generally followed clinically and examined electromyographically.
Nerve grafting has been reported unsuccessful if the grafts are more than 6 cm in length, 8,10,11 as this is the case in most traumatic longitudinal nerve traction injuries. Tibial tendon transfer has been shown to improve patients' mobility/ambulation without assistive devices. However, tendon transfer has been reported to provide only weaker dorsiflexion and gait. 12 We report here the results of a retrospective analysis of surgically managed 21 patients who had knee injuries and foot drop.

METHODS AND PATIENTS
This is a retrospective study of a series of 21 consecutive patients (12 females and 8 males) with knee injuries and foot drop. Patients in our present study underwent peroneal or tibial nerve transfer with us between 2006 and 2015. The lead author (R.K.N.) 13 performed decompression, internal neurolysis, and external neuroplasty of the affected peroneal nerve in all patients and the tibial nerve in some patients. Furthermore, we transferred tibial or superficial peroneal nerve fascicles to the motor branch of the tibialis anterior and deep peroneal nerve. 13 Excision of neuroma of the deep peroneal nerve was also done in 1 patient. Intraoperative monitoring of the peroneal nerve was performed on the affected leg in all patients in this study.
Mean follow-up after the operation was 19 months (range, 6-50 months). The mean age was 44 years (range, 17-77 years). For all patients, the preoperative clinical examination and electromyographic evaluation were performed. Nerve conduction and clinical function results showed injury to the peroneal nerve in all patients. Preoperative duration of injury and foot drop (1-17 months) reported by these patients was recorded for all patients except one. Further patient demographics, including age, gender, mechanism, and extent of the injury, are provided in Table 1.
The lead author (R.K.N.) clinically evaluated ankle eversion, inversion, dorsiflexion, and plantar flexion using Modified British Medical Research Council Motor Scale (BMRC) for muscle strength preoperatively and at least 6 months after surgery. This was a retrospective study of patient charts, which exempted it from the need for institutional review board approval in the United States. Patients were treated ethically in compliance with the Helsinki declaration. Documented informed consent was obtained for all patients.

Statistical analysis
Statistical analysis was performed using Analyse-It plugin (Leeds, United Kingdom) for Microsoft Excel 2003 software. A P value of less than .05 was considered as statistically significant.

RESULTS
Our patients in this study had peroneal nerve injuries and foot drop resulting from mostly lumbar surgical procedures, accidents, and gunshot wounds. The outcomes of the injured foot movements for each of these 21 patients are shown separately in Table 1. Foot movements from tibial nerve innervations are toe flexion, plantar flexion, and ankle inversion. These were not greatly affected and therefore no significant changes after the surgery. Foot movements from peroneal nerve innervations are ankle dorsiflexion and eversion. These foot functions were severely damaged to mean BMRC 1.1 as compared with the normal value of BMRC 5.0. Overall statistically significant clinical improvement of ankle dorsiflexion, eversion, and plantar flexion from preoperative BMRC grade 2.6 ± 0.5 to postoperative BMRC grade 3.6 ± 0.7 (P = .0000004) was achieved ( Table 2).
Of 21 patients who had no ankle dorsiflexion (BMRC 0/5) preoperatively, at least after 6 months of nerve transfer, the outcome was excellent in 9 patients. They had ankle dorsiflexion of BMRC 4/5 and greater (4+/5) and achieved normal gait, indicating that these 9 patients fully recovered anterior tibialis muscle function. In 7 patients, there was significant improvement of dorsiflexion from BMRC 0/5 preoperatively to BMRC 2+ to 3/5 postoperatively and ankle eversion (BMRC 2/5 to 4/5 preoperatively). Some of these patients did not gain complete antigravity, and they were using AFO and braces. Ankle dorsiflexion did not improve in 4 patients. They were considered for tendon transfer (Figs 1-3).

DISCUSSION
The common peroneal nerve is the most frequently injured nerve in knee dislocation and foot drop, due to lack of intraneural vessels and inconsistent blood supply around fibular neck. 14 We and other investigators compared and reported the benefits and drawbacks of various foot drop managements. 13  Users of AFOs have been found unsatisfied and noncompliant with the device because of discomfort, hygiene, and mobility issues. 17,18 Flores et al 19 reported that the transfer of the soleus muscle to the deep peroneal nerve demonstrated poor results in most of their patients. Although posterior tibial tendon transfer does not improve ankle dorsiflexion significantly and has long-term complications, it has been considered as a reasonable treatment option. 20,21 Nerve grafting is rarely successful when grafts are greater than 6 cm in length. 8,10,11 Peskun et al 22 found gender (male) as one of the significant risk factors associated with peroneal nerve injury. This is not the case in our present study and might be due to a fewer patients. However, their study did not find that age or mechanism of injury is a predictive risk factor of peroneal nerve injury as shown by Giuffre et al 16 , who showed a trend toward a more favorable outcome in younger patients. Our present study results also do not show any trend of better outcome only in younger patients. In our experience of management of patients with foot drop, older patients, both male and female (52, 53, 54, 57, 64, 77 years of age), also gained ankle dorsiflexion to BMRC 3 and 4 from BMRC 0 after they had nerve transfer procedure. Furthermore, Giuffre et al 16 compared mechanism of injury ePlasty VOLUME 17 (high and low energy) with our previously published report on this subject. 13 They claim that their patients had high-energy trauma, whereas most of our patients had low-energy injuries. 16 In addition, they reported that mechanisms of injury have statistically significant effect on the outcome of the surgery. 16 We disagree with their statements that our patients had low-energy trauma, as all our present study patients had no ankle dorsiflexion (BMRC 0/5) preoperatively. However, overall statistically significant clinical improvement of ankle dorsiflexion and eversion of BMRC 3.6/5 was achieved postoperatively in our present study of patients with foot drop. Nerve grafts less than 6 cm in length has been shown to achieve antigravity or greater ankle dorsiflexion function in an operative management for common peroneal neuropathy in a series of 318 patients. 23 Foot movements such as toe extension, ankle dorsiflexion, and ankle eversion (peroneal nerve functions) were very poor (BMRC 1.1/5) preoperatively. Moreover, there was no ankle dorsiflexion (BMRC 0/5) preoperatively in all our patients with foot drop in this study. This indicates that the peroneal nerve injury was severe in our present study patients, unlike Gifurre et al, 16 stated about the severity of peroneal nerve injury in our patients with foot drop in our previous report. 13

CONCLUSION
Overall statistically significant clinical improvement of ankle dorsiflexion, eversion, and toe extension was achieved in 80% of our study patients. Most of these patients gained antigravity and were able to walk with minimal steppage gait. In the other 4 patients (20%), there was good improvement in ankle eversion but poor or no ankle dorsiflexion.

AUTHOR CONTRIBUTIONS
R.K.N. conceived of the study, performed all the surgical procedures, and revised the manuscript. C.S. participated in the design of the study, gathered data, performed the statistical analysis, and drafted the manuscript. Both authors read and approved the final manuscript. ePlasty VOLUME 17